$htmlFontSize: 10px;
html{
font-size: $htmlFontSize;
}
@function strip-unit($number){
    @return $number / ($number*0 +1);
}
@function add-rem-unit($number){
        $htmlfs: strip-unit($htmlFontSize);
        $num: strip-unit($number);
        @return  ($num / $htmlfs)* 1rem;
}

@mixin sprite-dimensions($map, $sprite) {
      height: add-rem-unit(image-height(sprite-file($map, $sprite)));
      width: add-rem-unit(image-width(sprite-file($map, $sprite)));
}